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/OpenJDK 21

Class RecordingStream

java.lang.Object
jdk.jfr.consumer.RecordingStream
All Implemented Interfaces:
AutoCloseable, EventStream
public final class RecordingStream extends Object implements AutoCloseable, EventStream
A recording stream produces events from the current JVM (Java Virtual Machine).

The following example shows how to record events using the default configuration and print the Garbage Collection, CPU Load and JVM Information event to standard out.

Configuration c = Configuration.getConfiguration("default");
try (var rs = new RecordingStream(c)) {
    rs.onEvent("jdk.GarbageCollection", System.out::println);
    rs.onEvent("jdk.CPULoad", System.out::println);
    rs.onEvent("jdk.JVMInformation", System.out::println);
    rs.start();
}
Since:
14

Constructor Summary

Constructor Description
RecordingStream()
Creates an event stream for the current JVM (Java Virtual Machine).
RecordingStream(Configuration configuration)
Creates a recording stream using settings from a configuration.

Method Summary

Modifier and Type Method Description
void awaitTermination()
Blocks until all actions are completed, or the stream is closed, or the current thread is interrupted, whichever happens first.
void awaitTermination(Duration timeout)
Blocks until all actions are completed, or the stream is closed, or the timeout occurs, or the current thread is interrupted, whichever happens first.
void close()
Closes this resource, relinquishing any underlying resources.
EventSettings disable(Class<? extends Event> eventClass)
Disables event.
EventSettings disable(String name)
Disables event with the specified name.
void dump(Path destination)
Writes recording data to a file.
EventSettings enable(Class<? extends Event> eventClass)
Enables event.
EventSettings enable(String name)
Enables the event with the specified name.
void onClose(Runnable action)
Registers an action to perform when the stream is closed.
void onError(Consumer<Throwable> action)
Registers an action to perform if an exception occurs.
void onEvent(String eventName, Consumer<RecordedEvent> action)
Registers an action to perform on all events matching a name.
void onEvent(Consumer<RecordedEvent> action)
Registers an action to perform on all events in the stream.
void onFlush(Runnable action)
Registers an action to perform after the stream has been flushed.
boolean remove(Object action)
Unregisters an action.
void setEndTime(Instant endTime)
Specifies the end time of the stream.
void setMaxAge(Duration maxAge)
Determines how far back data is kept for the stream.
void setMaxSize(long maxSize)
Determines how much data is kept for the stream.
void setOrdered(boolean ordered)
Specifies that events arrives in chronological order, sorted by the time they were committed to the stream.
void setReuse(boolean reuse)
Specifies that the event object in an EventStream.onEvent(Consumer) action can be reused.
void setSettings(Map<String,String> settings)
Replaces all settings for this recording stream.
void setStartTime(Instant startTime)
Specifies the start time of the stream.
void start()
Starts processing of actions.
void startAsync()
Starts asynchronous processing of actions.
boolean stop()
Stops the recording stream.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods declared in interface jdk.jfr.consumer.EventStream

onMetadata

Constructor Details

RecordingStream

public RecordingStream()
Creates an event stream for the current JVM (Java Virtual Machine).
Throws:
IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed)
SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

RecordingStream

public RecordingStream(Configuration configuration)
Creates a recording stream using settings from a configuration.

The following example shows how to create a recording stream that uses a predefined configuration.

var c = Configuration.getConfiguration("default");
try (var rs = new RecordingStream(c)) {
    rs.onEvent(System.out::println);
    rs.start();
}
Parameters:
configuration - configuration that contains the settings to use, not null
Throws:
IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed)
SecurityException - if a security manager is used and FlightRecorderPermission "accessFlightRecorder" is not set.
See Also:

Method Details

enable

public EventSettings enable(String name)
Enables the event with the specified name.

If multiple events have the same name (for example, the same class is loaded in different class loaders), then all events that match the name are enabled. To enable a specific class, use the enable(Class) method or a String representation of the event type ID.

Parameters:
name - the settings for the event, not null
Returns:
an event setting for further configuration, not null
See Also:

setSettings

public void setSettings(Map<String,String> settings)
Replaces all settings for this recording stream.

The following example records 20 seconds using the "default" configuration and then changes settings to the "profile" configuration.

Configuration defaultConfiguration = Configuration.getConfiguration("default");
Configuration profileConfiguration = Configuration.getConfiguration("profile");
try (var rs = new RecordingStream(defaultConfiguration)) {
    rs.onEvent(System.out::println);
    rs.startAsync();
    Thread.sleep(20_000);
    rs.setSettings(profileConfiguration.getSettings());
    Thread.sleep(20_000);
}
Parameters:
settings - the settings to set, not null
See Also:

enable

public EventSettings enable(Class<? extends Event> eventClass)
Enables event.
Parameters:
eventClass - the event to enable, not null
Returns:
an event setting for further configuration, not null
Throws:
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event

disable

public EventSettings disable(String name)
Disables event with the specified name.

If multiple events with same name (for example, the same class is loaded in different class loaders), then all events that match the name are disabled. To disable a specific class, use the disable(Class) method or a String representation of the event type ID.

Parameters:
name - the settings for the event, not null
Returns:
an event setting for further configuration, not null

disable

public EventSettings disable(Class<? extends Event> eventClass)
Disables event.
Parameters:
eventClass - the event to enable, not null
Returns:
an event setting for further configuration, not null
Throws:
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event

setMaxAge

public void setMaxAge(Duration maxAge)
Determines how far back data is kept for the stream.

To control the amount of recording data stored on disk, the maximum length of time to retain the data can be specified. Data stored on disk that is older than the specified length of time is removed by the Java Virtual Machine (JVM).

If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely if events are on

Parameters:
maxAge - the length of time that data is kept, or null if infinite
Throws:
IllegalArgumentException - if maxAge is negative
IllegalStateException - if the recording is in the CLOSED state

setMaxSize

public void setMaxSize(long maxSize)
Determines how much data is kept for the stream.

To control the amount of recording data that is stored on disk, the maximum amount of data to retain can be specified. When the maximum limit is exceeded, the Java Virtual Machine (JVM) removes the oldest chunk to make room for a more recent chunk.

If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely.

The size is measured in bytes.

Parameters:
maxSize - the amount of data to retain, 0 if infinite
Throws:
IllegalArgumentException - if maxSize is negative
IllegalStateException - if the recording is in CLOSED state

setReuse

public void setReuse(boolean reuse)
Description copied from interface: EventStream
Specifies that the event object in an EventStream.onEvent(Consumer) action can be reused.

If reuse is set to true, an action should not keep a reference to the event object after the action has completed.

Specified by:
setReuse in interface EventStream
Parameters:
reuse - true if an event object can be reused, false otherwise

setOrdered

public void setOrdered(boolean ordered)
Description copied from interface: EventStream
Specifies that events arrives in chronological order, sorted by the time they were committed to the stream.
Specified by:
setOrdered in interface EventStream
Parameters:
ordered - if event objects arrive in chronological order to EventStream.onEvent(Consumer)

setStartTime

public void setStartTime(Instant startTime)
Description copied from interface: EventStream
Specifies the start time of the stream.

The start time must be set before starting the stream

Specified by:
setStartTime in interface EventStream
Parameters:
startTime - the start time, not null
See Also:

setEndTime

public void setEndTime(Instant endTime)
Description copied from interface: EventStream
Specifies the end time of the stream.

The end time must be set before starting the stream.

At end time, the stream is closed.

Specified by:
setEndTime in interface EventStream
Parameters:
endTime - the end time, not null
See Also:

onEvent

public void onEvent(String eventName, Consumer<RecordedEvent> action)
Description copied from interface: EventStream
Registers an action to perform on all events matching a name.
Specified by:
onEvent in interface EventStream
Parameters:
eventName - the name of the event, not null
action - an action to perform on each RecordedEvent matching the event name, not null

onEvent

public void onEvent(Consumer<RecordedEvent> action)
Description copied from interface: EventStream
Registers an action to perform on all events in the stream.

To perform an action on a subset of event types, consider using EventStream.onEvent(String, Consumer) and EventStream.onMetadata(Consumer) as it is likely more performant than any selection or filtering mechanism implemented in a generic action.

Specified by:
onEvent in interface EventStream
Parameters:
action - an action to perform on each RecordedEvent, not null
See Also:

onFlush

public void onFlush(Runnable action)
Description copied from interface: EventStream
Registers an action to perform after the stream has been flushed.
Specified by:
onFlush in interface EventStream
Parameters:
action - an action to perform after the stream has been flushed, not null

onClose

public void onClose(Runnable action)
Description copied from interface: EventStream
Registers an action to perform when the stream is closed.

If the stream is already closed, the action will be performed immediately in the current thread.

Specified by:
onClose in interface EventStream
Parameters:
action - an action to perform after the stream is closed, not null
See Also:

onError

public void onError(Consumer<Throwable> action)
Description copied from interface: EventStream
Registers an action to perform if an exception occurs.

If an action is not registered, an exception stack trace is printed to standard error.

Registering an action overrides the default behavior. If multiple actions have been registered, they are performed in the order of registration.

If this method itself throws an exception, resulting behavior is undefined.

Specified by:
onError in interface EventStream
Parameters:
action - an action to perform if an exception occurs, not null

close

public void close()
Description copied from interface: AutoCloseable
Closes this resource, relinquishing any underlying resources. This method is invoked automatically on objects managed by the try-with-resources statement.
Specified by:
close in interface AutoCloseable
Specified by:
close in interface EventStream

remove

public boolean remove(Object action)
Description copied from interface: EventStream
Unregisters an action.

If the action has been registered multiple times, all instances are unregistered.

Specified by:
remove in interface EventStream
Parameters:
action - the action to unregister, not null
Returns:
true if the action was unregistered, false otherwise
See Also:

start

public void start()
Description copied from interface: EventStream
Starts processing of actions.

Actions are performed in the current thread.

To stop the stream, use the EventStream.close() method.

Specified by:
start in interface EventStream

startAsync

public void startAsync()
Starts asynchronous processing of actions.

Actions are performed in a single separate thread.

To stop the stream, use the close() method.

The following example prints the CPU usage for ten seconds. When the current thread leaves the try-with-resources block the stream is stopped/closed.

try (var stream = new RecordingStream()) {
    stream.enable("jdk.CPULoad").withPeriod(Duration.ofSeconds(1));
    stream.onEvent("jdk.CPULoad", event -> {
        System.out.println(event);
    });
    stream.startAsync();
    Thread.sleep(10_000);
}
Specified by:
startAsync in interface EventStream
Throws:
IllegalStateException - if the stream is already started or closed

stop

public boolean stop()
Stops the recording stream.

Stops a started stream and waits until all events in the recording have been consumed.

Invoking this method in an action, for example in the onEvent(Consumer) method, could block the stream indefinitely. To stop the stream abruptly, use the close() method.

The following code snippet illustrates how this method can be used in conjunction with the startAsync() method to monitor what happens during a test method:

AtomicBoolean socketUse = new AtomicBoolean();
try (var r = new RecordingStream()) {
    r.setMaxSize(Long.MAX_VALUE);
    r.enable("jdk.SocketWrite").withoutThreshold();
    r.enable("jdk.SocketRead").withoutThreshold();
    r.onEvent(event -> socketUse.set(true));
    r.startAsync();
    testFoo();
    r.stop();
    if (socketUse.get()) {
        r.dump(Path.of("socket-events.jfr"));
        throw new AssertionError("testFoo() should not use network");
    }
}
Returns:
true if recording is stopped, false otherwise
Throws:
IllegalStateException - if the recording is not started or is already stopped
Since:
20

dump

public void dump(Path destination) throws IOException
Writes recording data to a file.

The recording stream must be started, but not closed.

It's highly recommended that a max age or max size is set before starting the stream. Otherwise, the dump may not contain any events.

Parameters:
destination - the location where recording data is written, not null
Throws:
IOException - if the recording data can't be copied to the specified location, or if the stream is closed, or not started.
SecurityException - if a security manager exists and the caller doesn't have FilePermission to write to the destination path
Since:
17
See Also:

awaitTermination

public void awaitTermination(Duration timeout) throws InterruptedException
Description copied from interface: EventStream
Blocks until all actions are completed, or the stream is closed, or the timeout occurs, or the current thread is interrupted, whichever happens first.
Specified by:
awaitTermination in interface EventStream
Parameters:
timeout - the maximum time to wait, not null
Throws:
InterruptedException - if interrupted while waiting
See Also:

awaitTermination

public void awaitTermination() throws InterruptedException
Description copied from interface: EventStream
Blocks until all actions are completed, or the stream is closed, or the current thread is interrupted, whichever happens first.
Specified by:
awaitTermination in interface EventStream
Throws:
InterruptedException - if interrupted while waiting
See Also:

© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/jdk.jfr/jdk/jfr/consumer/RecordingStream.html